In alt.home.repair on Sat, 02 Aug 2003 13:51:53 -0400 meirman
posted:
In alt.home.repair on Thu, 01 Aug 2003 17:04:11 "HvacTech2"
posted:
Hi 'nuther, hope you are having a nice day
On 01-Aug-03 At About 09:01:39, 'nuther Bob wrote to All
Subject: Thermostat Wiring
'B From: 'nuther Bob
'B On Thu, 01 Aug 2003 05:16:08 , "HvacTech2"
'B wrote:
'B If only it were that simple, but of course it isn't. by doing
'B what he wants to do the A/C would run at the same time which could
'B easily damage his compressor. and no, I do not give answers so
'B someone can damage their system.
'B Yeah, but he posted this in a followup:
'B "What I actually want to do is put in a second On/Auto switch for the
'B fan - in parallel with the existing switch. (Don't ask why.) One
'B side of the new switch should be wired to the green wire terminal.
'B The other side of the new switch wired to what???"
'B So, he's got a fan switch already. All he has to do is mimic that
'B switch.
Sorry you are wrong. I of course cannot see what he has but most thermostats
use a Y to G internal connection inside to run the fan when the A/C comes on.
I think the terminology here might be a problem. On the thermostats
I've used, if you turn the fan switch to ON**, the fan runs whether
the A/C is on or not. The A/C might be enabled***, but unless the
house is hot enough that the the temperature setting is lower than the
house temperature at the thermostat, and the compressor is running, I
don't think most of us would say that the A/C has "come on".
***I"m not sure the industry term for this, but I mean by "enabled"
that the A/C is ready to run as soon as the house is hot enough to
cause the thermal switch to turn it on. What is the industry term for
this?
**Peter is trying to duplicate the ON setting for the fan
switch, not the AUTO setting.
Replying to my own post, the line above is important, but much of the
rest of my previous post wasn't.
To us, it's hard to understand when you say it runs the fan when the
A/C comes on, if it runs the fan all the time.
If there is an internal connection from the G to the Y, which is the
primary cool call relay, what would happen if that internal connection
was broken and the thermal part of the thermostat was relied on to
turn on the compressor? Would not the fan either stay on all the time
if the switch were in the ON position, or go on when it should if in
the Auto position?
if you parallel that, whenever you run the new switch you will run the A/C
and damage it.
Do you mean, because even though the fan and compressor are on,
eventually the house will be as cold as the A/C can make it, but it
will keep running? Would that damage it?
OK, I still can't guess what Hvac would say to this, but I've figured
out what he is getting at.
If you mean that would damage it, what happens if I use my current
thermostat and set my A/C on and my thermostat to 33 degrees, and my
fan on AUTO or ON?
And I can't figure out what Hvac would say to this, but I can explain
the rest of it.
Hvac is referring to a connection in the thermostat, at least
mechanical ones he seems to say, between the Y (Primary cool call
wire) and the Auto position of the fan switch. He's saying that when
the unit is on A/C and the fan is on AUTO, when the thermostat calls
for cooling and closes the connection from the Red to the Yellow, this
also provides power to the internal connection from the Yellow to the
AUTO position of the fan, and thus runs 24 volts to the Green, so that
the fan goes on.
But, Peter, if you run a the switch part of a relay in simple shunt
with the ON position of the Fan switch, the power will go (logically
only since it is AC current) in the opposite direction, compared to
the last sentence of the previous paragraph**. That is, when the relay
you add sends 24 volts to the Green wire, that 24 volts would be
present at the AUTO lead of the Fan switch. We know the Fan switch is
in the AUTO position, because if it were in the ON position, it would
be ON all the time anyhow and Peter would be asking how to turn it
off, not how to turn it on. When the 24 volts reaches the Fan switch
Auto position, it then goes through the switch to the common terminal
of the Fan switch. And then via the internal connection in the
thermostat, to the Yellow screw/wire, where it goes to the furnace and
activates the cooling relay and cooling function of the AC.
Peter, I think if you stop here for a minute you can figure out what
you need to do, but if you are impatient, meet me after the 7 line
footnote in the next line. Otherwise, pause here to think about it.
**If this were DC, this could be prevented by the use of a diode, but
it is AlternatingCurrent. In some devices, not necessarily Air
Conditioning, one could probably just rectify the whole thing, the
whole power supply, with a diode and then block the current from going
the opposite direction with a well-placed diode in the opposite
direction, but half wave rectification would lower the effective
voltage, require a bunch of testing to make sure everything still
worked, and there is no need for that here.
What to do next?
Use the relay you are controlling remotely to disconnect the Green
lead of the thermostat from the Green lead of the furnace.
In other words, take the Green lead from the furnace-AC and connect it
to the common connector of a double throw relay switch. In the normal
position, have it connected to the Green lead from the thermostat, as
it is now.****
In the activated position, have it connected to the Red lead from the
thermostat/furnace-AC. Of course you don't have to and can't cut the
Red wire.
You can make these connections anywhere along the wire from the
furnace to the thermostat. Probably easiest near the furnace. But
you know that.
Don't forget, if you do a bad job or use a really inferior relay,
that this could lead to the fan not running whether the relay is
activated OR NOT. I guess this is what Hvac is worried about. Don't
forget what you have done, if you ever have problems^^. Don't forget
if you sell the house^^^ to rip out what you've done and solder the
halves of green wire, or tell the next owner what you have done, and
remind him to tell the owner after him.
(I was once involved in a situation where I fiddled with phone lines,
and years after I left, the phone company had to run a whole new wire
from the basement to the second floor, becuase they couldn't figure it
out. I had restored it, but not fully.)
^^I've fiddled with the wires to my stereo, my burglar alasm, my vcr
and its output distribution, and my car until I've made them so
complicated I can't even remember all the wiring. I have to refresh my
memory every time I need to change things. The burglar alarm, at
least I drew myself a schematic. (The car has notes scattered through
the wiring diagram pages in the shop manual)
(Hvac made a reference to needing a double throw relay, but that is
not how I figured this out. It was his reference to the internal
connection. Peter, feel free to sue me if you are foolish enough to
connect this wrong in blind obedience to my directions, without
thinking about it and being convinced on your own that this will work.
How could it not if you do what I say? Anyone else, who has not
released me, may sue me also.
)
****As an aside, this setup would be referred to as Fail-Safe. Not
because it is a nuclear weapon where it will destroy the world if we
don't have rigid precautions. But because that compound word means
something specific. It means if your added relay fails, things will
return to normal, the Safe situation. The odds are very very high that
coil in it will de-energize and the relay will go back to its normal
position, and your wires will then be connected the way they were
before you fiddled with them. Of course, since this isn't an
explosive, you might want to reverse those wires so if it fails the
fan will always be on.
^^^I had a beautiful 1930 apartment in Brooklyn NY, with a separate
pipe next to the tub which controlled draining, not draining, and
overflow. In order to get a deeper bathtub, I taped up the overflow
holes, and got about 2 inches more. I was happy for 10 years, never
had an overflow, but I was afraid I would move out of the building
without undoing what I had done. But I remembered and did so the last
week I was there.
Here I have a modern little bathtub and I reversed the overlow plate,
to get about 1 1/2 inches more depth. I turned the overflow, inside
the tub, upside down. I hope I remember to undo it before I move,
although in Brooklyn, it was totally invisible -- there was no need to
pull the pipe up more than a quarter inch. Here one can see the open
drain at the top even before getting in the tub.
Even without modifying the thermostat, how come we don't damage our
A/C's when we have the A/C-Heat switch set to OFF and the Fan switch
set to AUTO or ON?
Or when we have the A/C-Heat switch set to A/C, the thermostat set to
100 degrees (or anything hotter than what the house is), and the Fan
switch set to AUTO or ON?
Can we damage our A/C just by setting the thermostat to settings we
don't always use?
-= HvacTech2 =-
Meirman
Meirman
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